Weird Issue with Making a Call

I called my son's phone yesterday but he said he did not receive any calls from me. I thought maybe he was Blocking my number but that was not the case. When I called his phone again while it was right in front of me his phone never rang. He was able to call my phone.

When I went to my Call Log and called from his missed call, his phone then rang.

Could this be a hardware issue with my phone? I do restart my phone daily BTW.